The present invention relates to the general field of making a blade out of composite material for a rotor wheel of a turbine engine. The invention relates more particularly to fabricating the root of such a blade.
The intended field is that of gas turbine rotor blades for aeroengines or for industrial turbines.
Proposals have already been made to make blades for turbine engines out of composite material, and in particular out of ceramic matrix composite (CMC) material. Reference may be made in particular to Document FR 2 939 129, which describes fabricating a turbine engine blade out of composite material comprising fiber reinforcement that is densified by a matrix. With such a method, the resulting blade presents in particular a root that is formed from a fiber strip extending in a direction that corresponds to the longitudinal direction of the blade.
Furthermore, in order to mount such a blade on a rotor disk, it is known to give the blade root the shape of a bulb. The blade root with its bulb shape co-operates with a slot of complementary shape formed in the periphery of the rotor disk in order to retain the blade radially on the disk by means of a dovetail-type connection.
When a blade is made out of composite material, the bulb shape of the blade root is generally obtained during the weaving of the fiber blank that is to constitute the blade by forming extra thickness in the blade root, this extra thickness subsequently being machined to the final shapes of the bulb. In practice, the extra thickness is usually obtained by adding an insert while weaving the fiber blank.
Nevertheless, such a method of fabricating a blade out of composite material with a bulb-shaped root presents numerous drawbacks. Making the insert and putting it into position during weaving of the fiber blank of the blade are operations that are very difficult. In addition, the attachment of the blade presents mechanical strength difficulties and it becomes degraded in fatigue by oxidation.
Also known, from Document FR 2 941 487, is a solution for mounting a composite material blade on a rotor disk in which the blade root is clamped between metal plates that are fastened together by means of a welded peg. With that solution, the main force retaining the blade on the rotor disk is taken up by shear in the peg and by compression against the hole in the composite material. Nevertheless, expansion differences between the metal of the plate and the composite material of the root give rise either to thermal shear stresses if the fastening is rigid, or to uncertainty about the positioning of the bearing plates if the fastening is provided with slack.